1. Field of the Invention
The present invention relates generally to plastic containers, and more particularly to hot-fillable containers having deformation resistant vacuum panels.
2. Related Art
The use of blow molded plastic containers for packaging “hot fill” beverages is known. In the process of filling a plastic container with hot liquid, pressure or vacuum imposed on the container can result in permanent deformation of the container. The sidewalls of the container can deform as the container is being filled with hot fluids. In addition, the rigidity of the container decreases after the hot fill liquid is introduced into the container. The temperatures employed in these operations can be above the Tg of the plastic used (for example PET), which can result in the deformation becoming permanent. In addition, as the liquid cools, gas that is also in the container shrinks in volume, producing a vacuum in the container.
Hot fill containers often have substantially rectangular vacuum panels that are designed to collapse inwardly as the contents of the container cool after the hot-fill process. These vacuum panels help reduce unwanted deformation of the container by flexing inward under the pressure of the vacuum. By flexing inward, the vacuum panels relieve pressure created by the vacuum and prevent or reduce the deformation of other parts of the container.
U.S. Pat. No. 5,341,946 shows vacuum panels having multiple outwardly projecting portions which are separated by a portion of the vacuum panel. U.S. Pat. Nos. 5,279,433 and 6,016,932 show other configurations of vacuum panels having projecting center portions. Yet another configuration of vacuum panels having projecting center portions is shown in WO 97/34808.
The invention addresses design problems inherent with the panel designs discussed in the above-referenced patents.